A wireless tire state monitoring device has been proposed that enables a driver to check the state of a plurality of tires provided on a vehicle while in a vehicle compartment. In this type of tire state monitoring device, a tire state detecting device that transmits a data signal associated with the tire state is arranged on each wheel. Furthermore, a receiver that receives the data signal from the tire state detecting device is arranged on a vehicle body. The tire state monitoring device specifies from which tire state detecting device of which one of the plurality of tires the received data signal is transmitted. In other words, the position of the wheel associated with the received data signal is specified in the receiver.
In patent document 1, on which one of the plurality of wheels each tire state detecting device is arranged is specified by using the ABS (Antilock Brake System). The tire state detecting device of each wheel transmits a transmission signal to the receiver when the wheel is at a rotation angle (hereinafter referred to as angle) determined in advance. The angle determined in advance is detected by an acceleration sensor, which rotates with the wheel. A gravitational acceleration value detected by the acceleration sensor changes between −1G and +1G while the wheel makes one rotation. The tire state detecting device transmits the transmission signal when the wheel is at the angle determined in advance based on the gravitational acceleration value detected by the acceleration sensor. The receiver detects a rotation position of the wheel by using the ABS at an instant of receiving the transmission signal. As mentioned above, the transmission signal is transmitted each time the wheel is at the angle determined in advance. Thus, when the rotation position of each wheel is detected at the instant of receiving the transmission signal, the rotation position of the wheel, where the tire state detecting device that transmitted the relevant transmission signal is arranged, becomes the same every time. Thus, on which one of the plurality of wheels each tire state detecting device is arranged can be specified.